CA2048323A1 - Process for producing molded bodies from precursors of oxidic high-temperature superconductors - Google Patents
Process for producing molded bodies from precursors of oxidic high-temperature superconductorsInfo
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- CA2048323A1 CA2048323A1 CA002048323A CA2048323A CA2048323A1 CA 2048323 A1 CA2048323 A1 CA 2048323A1 CA 002048323 A CA002048323 A CA 002048323A CA 2048323 A CA2048323 A CA 2048323A CA 2048323 A1 CA2048323 A1 CA 2048323A1
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/50—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on rare-earth compounds
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F1/00—Etching metallic material by chemical means
- C23F1/10—Etching compositions
- C23F1/14—Aqueous compositions
- C23F1/16—Acidic compositions
- C23F1/18—Acidic compositions for etching copper or alloys thereof
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
- C04B35/45—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/653—Processes involving a melting step
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N60/00—Superconducting devices
- H10N60/01—Manufacture or treatment
- H10N60/0268—Manufacture or treatment of devices comprising copper oxide
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- Chemical Kinetics & Catalysis (AREA)
- Inorganic Chemistry (AREA)
- Inorganic Compounds Of Heavy Metals (AREA)
- Superconductor Devices And Manufacturing Methods Thereof (AREA)
- Nitrogen And Oxygen Or Sulfur-Condensed Heterocyclic Ring Systems (AREA)
- Glass Compositions (AREA)
- Compositions Of Oxide Ceramics (AREA)
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- Superconductors And Manufacturing Methods Therefor (AREA)
- ing And Chemical Polishing (AREA)
Abstract
Process for producing molded bodies from precursors of oxidic high-temperature superconductors Abstract of the disclosure:
In the process for producing molded bodies from precur-sors of oxidic high-temperature superconductors of the BSCCO type, a copper mold of the desired shape which encloses a solidified bismuth strontium calcium cuprate melt is treated with a solution of a soluble compound containing sulfate anions, an aqueous mineral acid and an oxidizing agent until the copper mold is dissolved.
In the process for producing molded bodies from precur-sors of oxidic high-temperature superconductors of the BSCCO type, a copper mold of the desired shape which encloses a solidified bismuth strontium calcium cuprate melt is treated with a solution of a soluble compound containing sulfate anions, an aqueous mineral acid and an oxidizing agent until the copper mold is dissolved.
Description
;~0483~3 The melt synthesis of high-temperature superconductor materials based on bismuth strontium calcium cuprate is described in DE 3,830,092 Al. The "BSCCO" high-tempera-ture superconductors which can be prepared according thereto or in another known manner have the composition Bi2(Sr,Ca)3Cu20~ 2-layer compound~), the ratio of strontium to calcium being (2 to 5) : 1 (BSCCO stands for bismuth strontium calcium copper oxide). In addition, "l-layer compounds~, Bi2(Sr,Ca)2CuO~, and ~3-layer com-pounds~, Bi2(Sr,Ca) 4CU30~, are known as ~SCCO high-tempera-ture superconductors. The oxygen index "x" is set by the sum of the valencies of Bi, Sr, Ca and Cu, but is vari-able to the extent that Bi may be tri- or pentavalent and Cu may be mono- or divalent.
DE 3,830,09~ Al also mentions the production of molded bodies from the bismuth strontium calcium cuprates. Such molded bodies can be obtained, for example, by casting in variously shaped molds which are preferably composed of copper if the mold i8 open as, for example, in the case of a cavity having inclined sidewalls or a half cylinder and permits the removal of the ca3ting in terms of shape.
It is also important that the ca~ting is carried out with the mold col~ so that the solidifying melt cools so rapidly at the mold wall that a chemical reaction with the copper of the mold wall doe~ not occur. Even if the mold wall is flexible and is composed, for example, of a thin metal sheet which can be bent aside after cooling, there are no problems.
20~8323 Substantially more difficult is the production of more complicated molded ~odies which necessitate a substan-tially closed mold possibly having a complicated shape.
In such cases, even the principle of a rapid cooling to avoid the wall reaction cannot always be used because the mold possibly has to be preheated to avoid an unduly premature solidification of the melt flowing in. In comparatively simple cases, for example in the production of fairly thick cylindrical molded bodies by casting in a tubular mold, a mechanical removal of the casing material is still conceivable, for instance by separating the mold wall into two half shells. However, this is no longer an attractive process even for relatively small diameters and can no longer be used in the case of complicated geometries such as rings or coils.
In order to convert a melt of the composition correspond-ing to the high-temperature superconductor into the superconducting state after solidification, a subseq~ent heat treatment of the solidified melt of 6 to 30 hours duration at temperatures around 800C in air or oxygen is necessary. However, only one metal is known which is suitable as casing material for BSCCO high-temperature superconductors and i8 permeable to oxygen at the heat treatment temperatures and, consequently, makes possible the conversion of the solidified melt into the desired high-temperature superconductor inside the metal casing:
silver. Unfortunately, at 960.8C, the melting point of silver is below the temperature at which the superconductor melt has to be in order to be capable of being reliably cast. Thus, a silver mold would melt before the superconductor melt had solidified.
For this reason, it is necessary to resort to copper molds since copper is the only system-immanent metal which is suitable for the present purpose. However, a removal of the copper from the solidified melt is ah-solutely necessary.
Since the mechanical stripping of the copper mold is only of limited practicability, its chemical dissolution suggests itself. In principle, this is possible with the aid of an oxidizing acid or an acid plus oxidizing agent.
Experiments of this type are known in connection with the investigation of yttrium barium cuprate superconductor powders which had been poured into copper tubes and compacted by deep drawing and rolling.
If, however, it i8 desired to proceed in the same manner in the case of bismuth-based superconductors, a strong attack of the acid on the superconductor or its precursor of the solidified melt is observed as soon as the copper casing is dissolved at one point and the surface of the solidified melt iB laid bare. Specifically, it iB found that the superconducting bismuth compounds are acid-soluble.
The ob~ect of the present invention is to provide a ~ 4 - ~048323 method which makes it possible to dissolve the copper casing without appreciably attacking the underlying superconductor or its precursor.
This object was achieved by adding sulfate ions to the solution containing the oxidizing acid or a non-oxidizing acid and an oxidizing agent. The principle underlying this invention is the formation of a protec-tive layer, which suppresses a further attack of the acid upon the superconducting compound, composed of strontium sulfate and/or calcium sulfate from the sulfate added to the electrolyte and the alkaline earth metals contained in the superconducting compound.
In particular, the invention therefore relates to a process for producing molded bodies from precursors of oxidic high-temperature superconductors of the BSCC0 t~tpe, which comprises treating a copper mold of the desired shape which encloses a solidified bismuth stron-tium calcium cuprate melt with a solution of a soluble compound containing sulfate anions, an aqueous mineral acid and an oxidizing agent until the copper mold is dissolved.
In addition, the process of the invention may preferably or optionally be one whe~ein a) the sulfates of sodium, potassium, ammonium, magnesium or zinc are used as soluble compound containing sulfate anions;
~ 5 ~ 204~323 b) hydrochloric acid or phosphoric acid is used as mineraL acid;
c) hydrogen peroxide or alkali chlorate is used as oxidizing agent;
d) nitric acid is simultaneously used as aqueous mineral acid and oxidizing agent, e) sulfuric acid is simultaneously used as aqueous mineral acid and as compound containing sulfate anions;
f) the copper mold is dissolved with a solution of aqueous nitric acid and sodium sulfate;
g) the copper mold is dissolved with a solution of aqueous sulfuric acid and hydrogen peroxide;
h) the treatment is carried out at 15 to 80C;
i) a copper mold is treated which encloses the solidi-fied bismuth strontium calcium cuprate melt and has one or more openings.
The amount of the compound containing sulfate anLons to be used ma~ be small per se and it is only necessary for the solubility product of calcium sulfate and strontium sulfate to be exceeded in the presence of mineral acid and oxidizing agent and at the selected temperature. Even 2 g of soluble sulfate compound, for example NaaS04, per liter of solution clearly exhibit the desired effects, but preferably concentrations of 100 to 300 g of soluble sulfate compound per liter of solution are employed.
The acid concentration, the treatment temperature and the - 6 - ~0~323 treatment time are not crucial. In general, low acid concentration and low treatment temperature require a longer treatment time and vice versa. In other respects, the treatment time depends decisively on the thickness of the mold wall to be dissolved.
For example, 10 to 32 % by weight HN03, IO to 20 % by weight HCl or 10 to 35 ~ by weight H2S04 can be employed, but without being tied to these limits. The concentration of the oxidizing agent, for example of the hydrogen peroxide, plays a role to an equally small extent. It is only necessary to ensure that H202 is also constantly present in addition to the nonoxidizing mineral acid.
H202, must therefore be gradually added, if necessary, in several portions.
It is, of course, within the scope of this invention if, in the case of somewhat thicker copper ~old walls (for in~tance, above 0.5 mm), a larger proportion of the copper is dissolved, for example, in pure nitric acid and, if necessary, ~lso at elevat0d temperature, but in the absence of sulfate ions and only then, when there is a danger of a local breakthrough of the superconductor 3urface, i8 a changeover made to the process according to the invention. In the absence of sulfate ions, the open end walls may be sealed, for example, with wax and thus be protected against the attack of the nitric acid. In this manner pure copper nitrate solutions are obtained which are not contaminated by sulfate. In addition, the ~ 7 ~ ~0~83Z3 copper mold is in total dissolved in a shorter time.
The process according to the invention is described in more detail below with reference to the embodiment using nitric acid:
The attack of nitric acid on the solidified supercon-ductor melt depends, for a given nitric acid conrentra-tion and at room temperature, on the concentration of sulfate ions in the solution. Table 1 shows the losses in weight (in % of the initial weight) for a compact cylind-rical test piece having a length of 14 mm and a diameter of 7mm (surface: 3.86 cm2),with the etchingsolution con-taining 10 ~ by weight of nitric acid and 0 to 500 g~
sodium sulfate. The experiment was carried out at room temperature.
- 8 - Z~323 Inhibitory action of sodium sulfate additions on the dissolution of BSCCO 2212 (Bi2SraCaCu2O~) in nitric acid (10%) .
Na2SO4 Weight loss (%) after (anhydrous) No. g.l~l 5~ 15~ 30~ 1 h 2 h 4 h 8 h 1 0 3.2 9.6 18.9 30.4 43.768.1 n.d.
2 100 0.1 0.15 0.23 0.32 0.390.50 0.65 3 200 0 0 0.02 0.15 0.320.76 1.42 4 300 0 0 0.04 0.12 0.260.45 0.90 400 0 0 0 0 0 0.04 0.16 6 500 0 0 0 0 0 0.03 0.08 -n . d . - not determined Adding sodium sulfate to 10 ~ nitric acid doe~, however, also reduce the rate of dissoLution of the copper:
- 9 - ~:0~8323 Dissolution of an empty copper tube piec~ having a comparable surface to that of BSCCO 2212 in Table 1 at various sodium sulfate concentrations Na2SO4 Weight loss (%) after (anhydrous) No. g ~ 30' 2 h 8 h 1 0 0.3 3.8 11 2 100 0.1 0.6 3.3 3 200 0.04 0.26 1.
With 10% nitric acld and 100 g of sodium sulfate, a substantial protection of the BSCCO core is already achieved, but the rates of dissolution of the copper are s,till very low for technical purposes. If 20~ nitric acid is used, the conditions which are shown in Table 3 both for the dis.solution of BSCCO and for that of copper (in brackets) are more favorable.
X:0~3323 Inhibitory action of sodium sulfate on the dissolution of BSCC0 2212 and copper (...~ in 20 % nitric acid at room temperature Na2SO4 Loss in weight (%) after (anhydrous) No. g ~ 15' 30' 1 h 2 h 4 h 8 h 1 0 25 (18) 44 (34) 72 (60) 100(100) 100(100) 100(100) 2 100 1.7(12) 2 (23) 2.3(42) 2.5( 87) 2.7(100) 3.0(100) 3 200 0.2( 9) 0.2(18) 0.4(35) 0.7( 74) 0.9(100) 1.3(100) 4 300 0 ( 6) 0 (13) 0 (25) 0 (52)0.2( 79) 0.2(100) 400 0 ( 4) 0 ( 9) 0 (17) 0 (31)0 ( 40) 0.2(52) 6 500 0 ( 2) 0 ( 4) 0 ( 7) 0 ( 9)0 ( 12) 0 ( 18) The di~solution in 32% nitric acid at room temperature i~ shown in Table 4 (with the values for copper again in brackets):
- 11- 20~8323 Inhibitory action of sodium sulfate on the dissolution of BSCC0 2212 and copper (...) in 32% nitric acid at room temperature Na2S04 Loss in weight (%) after (anhydrous) No.g ~ 15' 30' 1 h 2 h 4 h _ 1 100 0.51 (71) 1.7 (100) 4.4 (100) 9 (100) 20(100) 2<200+ 0.13 (38) 0 ( ~5) 0.12( 59) 3 ( 70) 9( 87) . .. . .. . _ _ . :, ., . :
+200 g of Na2S04 are no longer completely soluble in 32%
The~e experiments show that a combination of 20% nitric acid with 200 to 300 g of sodium sulfate are a sort of optlmum with which a still usable rate of dis~olution is accompanied by a good protective action. Of course, with continuous vi~ual inspection, 32% nitric acid with 100 g of sodium sulfate is also suitable. However, copper dissolves much more slowly in a solution saturated with sodium sulfa~e becauqe, with increasing dissolution of the copper, copper sulfate also crystallizes out im-mediately and readily deposits on the copper surface, inhibiting or rendering uneven the further dissolution.
Elevated temperature:
The effect of elevated temperature was examined in 10%
nitric acid:
Inhibitory action of NazS04 on the dissolution of BSCC0 2212 and copper in 10~ nitric acid at 70C (values for copper in brackets) Na2S04 Loss in weight (X) after (anhydrous) No. g~ 15' 30' 1 h 2 h 4 h 8 h 1 100 0.45(17) 0.77(32)1.1 (59)1.4(100)2.1(100) 2.9(100) 2 300 0 ( 3) 0.16( 7) 0.22(14)0.5( 27)0.7( 58) 0.7( 92) 3 500 0 ( 0) 0 ( 0)0 ( 0) - - -. . _ .. ._.
Here again favorable results are obtained with 100 to 300 g of sodium sulfate in a liter. They are e~sentiaLly equivalent to those which are obtained at room tempera-ture with 20% nitric acid.
In principle, other solutions which have the same effect as nitric acid are also conceivable:
a) Sulfuric acid + hydrogen peroxide b) Hydrochloric acid + hydrogen peroxide c) Hydrochloric acid + alkali chlorate - 13 Z0~L83Z3 The suitability of the combination of sulfuric acid with an oxidizing agent is demonstrated using 20~ sulfuric acid with 10% hydrogen peroxide at room tempexature. In this case, the addition of a sulfate is not necessary since the sulfate anions needed are provided by the sulfuric acid itself.
Differences in the dissolution of BSCC0 2212 and copper in 20% sulfuric acid with 10% H2O2 added at room temperature Tlme: 5~ 15~ 1 h 2 h 4 h Lo~s ~n weight of Cu/X 9.8 18 51 76 100 Los~ in weight of BSCCo/X 0.2 0.4 0.55 0.75 1.02 Example 1 (Comparative Example) A copper tube having a length of 10 cm, a wall thickness of 1 mm and an internal width of 8 mm, which contains a core composed of a qolidified BSCCO high-temperature superconductor melt of the formula Bi2Sr2CaCu20~, is placed in 20% nitric acid at room temperature and left there while stirring until the copper casing has been partlally etched away (2.8 h) and a part of the core is exposed.
The surface of the core exhibits deep holes and at the - 14 - 204~323 end faces, where the core was exposed to the action of the nitric acid without protection, it is dissolved away over a width of several mm.
Example 2 Example 1 was repeated, but 300 g of sodium sulfate were dissolved in one liter of 20% nitric acid. After 3 hours no breakthrough of the core was-as yet observable and a dense white film which covered the original surface had formed at the exposed end faces. After 12 hours, the copper had been dissolved down and the entire core was then covered with the white thin covering layer. Signs of an uneven removal or pitting were not observed.
Example 3 A similar rod to that in Example 1 was brought into contact with 200 ml of 20% sulfuric acid to which 30 ml of 10 % by weight hydrogen peroxide, divided into three equal portions, was gradually added, in which process copper was dissolved. The ~olution was stirred by means of a magnetic stirrer and the temperature was 25C. Ater 15 hours of contact time the copper casing had been dissolved. The superconductor core exhibited no acid attack on its surface, which was uniformly covered with alkaline earth metal sulfate.
DE 3,830,09~ Al also mentions the production of molded bodies from the bismuth strontium calcium cuprates. Such molded bodies can be obtained, for example, by casting in variously shaped molds which are preferably composed of copper if the mold i8 open as, for example, in the case of a cavity having inclined sidewalls or a half cylinder and permits the removal of the ca3ting in terms of shape.
It is also important that the ca~ting is carried out with the mold col~ so that the solidifying melt cools so rapidly at the mold wall that a chemical reaction with the copper of the mold wall doe~ not occur. Even if the mold wall is flexible and is composed, for example, of a thin metal sheet which can be bent aside after cooling, there are no problems.
20~8323 Substantially more difficult is the production of more complicated molded ~odies which necessitate a substan-tially closed mold possibly having a complicated shape.
In such cases, even the principle of a rapid cooling to avoid the wall reaction cannot always be used because the mold possibly has to be preheated to avoid an unduly premature solidification of the melt flowing in. In comparatively simple cases, for example in the production of fairly thick cylindrical molded bodies by casting in a tubular mold, a mechanical removal of the casing material is still conceivable, for instance by separating the mold wall into two half shells. However, this is no longer an attractive process even for relatively small diameters and can no longer be used in the case of complicated geometries such as rings or coils.
In order to convert a melt of the composition correspond-ing to the high-temperature superconductor into the superconducting state after solidification, a subseq~ent heat treatment of the solidified melt of 6 to 30 hours duration at temperatures around 800C in air or oxygen is necessary. However, only one metal is known which is suitable as casing material for BSCCO high-temperature superconductors and i8 permeable to oxygen at the heat treatment temperatures and, consequently, makes possible the conversion of the solidified melt into the desired high-temperature superconductor inside the metal casing:
silver. Unfortunately, at 960.8C, the melting point of silver is below the temperature at which the superconductor melt has to be in order to be capable of being reliably cast. Thus, a silver mold would melt before the superconductor melt had solidified.
For this reason, it is necessary to resort to copper molds since copper is the only system-immanent metal which is suitable for the present purpose. However, a removal of the copper from the solidified melt is ah-solutely necessary.
Since the mechanical stripping of the copper mold is only of limited practicability, its chemical dissolution suggests itself. In principle, this is possible with the aid of an oxidizing acid or an acid plus oxidizing agent.
Experiments of this type are known in connection with the investigation of yttrium barium cuprate superconductor powders which had been poured into copper tubes and compacted by deep drawing and rolling.
If, however, it i8 desired to proceed in the same manner in the case of bismuth-based superconductors, a strong attack of the acid on the superconductor or its precursor of the solidified melt is observed as soon as the copper casing is dissolved at one point and the surface of the solidified melt iB laid bare. Specifically, it iB found that the superconducting bismuth compounds are acid-soluble.
The ob~ect of the present invention is to provide a ~ 4 - ~048323 method which makes it possible to dissolve the copper casing without appreciably attacking the underlying superconductor or its precursor.
This object was achieved by adding sulfate ions to the solution containing the oxidizing acid or a non-oxidizing acid and an oxidizing agent. The principle underlying this invention is the formation of a protec-tive layer, which suppresses a further attack of the acid upon the superconducting compound, composed of strontium sulfate and/or calcium sulfate from the sulfate added to the electrolyte and the alkaline earth metals contained in the superconducting compound.
In particular, the invention therefore relates to a process for producing molded bodies from precursors of oxidic high-temperature superconductors of the BSCC0 t~tpe, which comprises treating a copper mold of the desired shape which encloses a solidified bismuth stron-tium calcium cuprate melt with a solution of a soluble compound containing sulfate anions, an aqueous mineral acid and an oxidizing agent until the copper mold is dissolved.
In addition, the process of the invention may preferably or optionally be one whe~ein a) the sulfates of sodium, potassium, ammonium, magnesium or zinc are used as soluble compound containing sulfate anions;
~ 5 ~ 204~323 b) hydrochloric acid or phosphoric acid is used as mineraL acid;
c) hydrogen peroxide or alkali chlorate is used as oxidizing agent;
d) nitric acid is simultaneously used as aqueous mineral acid and oxidizing agent, e) sulfuric acid is simultaneously used as aqueous mineral acid and as compound containing sulfate anions;
f) the copper mold is dissolved with a solution of aqueous nitric acid and sodium sulfate;
g) the copper mold is dissolved with a solution of aqueous sulfuric acid and hydrogen peroxide;
h) the treatment is carried out at 15 to 80C;
i) a copper mold is treated which encloses the solidi-fied bismuth strontium calcium cuprate melt and has one or more openings.
The amount of the compound containing sulfate anLons to be used ma~ be small per se and it is only necessary for the solubility product of calcium sulfate and strontium sulfate to be exceeded in the presence of mineral acid and oxidizing agent and at the selected temperature. Even 2 g of soluble sulfate compound, for example NaaS04, per liter of solution clearly exhibit the desired effects, but preferably concentrations of 100 to 300 g of soluble sulfate compound per liter of solution are employed.
The acid concentration, the treatment temperature and the - 6 - ~0~323 treatment time are not crucial. In general, low acid concentration and low treatment temperature require a longer treatment time and vice versa. In other respects, the treatment time depends decisively on the thickness of the mold wall to be dissolved.
For example, 10 to 32 % by weight HN03, IO to 20 % by weight HCl or 10 to 35 ~ by weight H2S04 can be employed, but without being tied to these limits. The concentration of the oxidizing agent, for example of the hydrogen peroxide, plays a role to an equally small extent. It is only necessary to ensure that H202 is also constantly present in addition to the nonoxidizing mineral acid.
H202, must therefore be gradually added, if necessary, in several portions.
It is, of course, within the scope of this invention if, in the case of somewhat thicker copper ~old walls (for in~tance, above 0.5 mm), a larger proportion of the copper is dissolved, for example, in pure nitric acid and, if necessary, ~lso at elevat0d temperature, but in the absence of sulfate ions and only then, when there is a danger of a local breakthrough of the superconductor 3urface, i8 a changeover made to the process according to the invention. In the absence of sulfate ions, the open end walls may be sealed, for example, with wax and thus be protected against the attack of the nitric acid. In this manner pure copper nitrate solutions are obtained which are not contaminated by sulfate. In addition, the ~ 7 ~ ~0~83Z3 copper mold is in total dissolved in a shorter time.
The process according to the invention is described in more detail below with reference to the embodiment using nitric acid:
The attack of nitric acid on the solidified supercon-ductor melt depends, for a given nitric acid conrentra-tion and at room temperature, on the concentration of sulfate ions in the solution. Table 1 shows the losses in weight (in % of the initial weight) for a compact cylind-rical test piece having a length of 14 mm and a diameter of 7mm (surface: 3.86 cm2),with the etchingsolution con-taining 10 ~ by weight of nitric acid and 0 to 500 g~
sodium sulfate. The experiment was carried out at room temperature.
- 8 - Z~323 Inhibitory action of sodium sulfate additions on the dissolution of BSCCO 2212 (Bi2SraCaCu2O~) in nitric acid (10%) .
Na2SO4 Weight loss (%) after (anhydrous) No. g.l~l 5~ 15~ 30~ 1 h 2 h 4 h 8 h 1 0 3.2 9.6 18.9 30.4 43.768.1 n.d.
2 100 0.1 0.15 0.23 0.32 0.390.50 0.65 3 200 0 0 0.02 0.15 0.320.76 1.42 4 300 0 0 0.04 0.12 0.260.45 0.90 400 0 0 0 0 0 0.04 0.16 6 500 0 0 0 0 0 0.03 0.08 -n . d . - not determined Adding sodium sulfate to 10 ~ nitric acid doe~, however, also reduce the rate of dissoLution of the copper:
- 9 - ~:0~8323 Dissolution of an empty copper tube piec~ having a comparable surface to that of BSCCO 2212 in Table 1 at various sodium sulfate concentrations Na2SO4 Weight loss (%) after (anhydrous) No. g ~ 30' 2 h 8 h 1 0 0.3 3.8 11 2 100 0.1 0.6 3.3 3 200 0.04 0.26 1.
With 10% nitric acld and 100 g of sodium sulfate, a substantial protection of the BSCCO core is already achieved, but the rates of dissolution of the copper are s,till very low for technical purposes. If 20~ nitric acid is used, the conditions which are shown in Table 3 both for the dis.solution of BSCCO and for that of copper (in brackets) are more favorable.
X:0~3323 Inhibitory action of sodium sulfate on the dissolution of BSCC0 2212 and copper (...~ in 20 % nitric acid at room temperature Na2SO4 Loss in weight (%) after (anhydrous) No. g ~ 15' 30' 1 h 2 h 4 h 8 h 1 0 25 (18) 44 (34) 72 (60) 100(100) 100(100) 100(100) 2 100 1.7(12) 2 (23) 2.3(42) 2.5( 87) 2.7(100) 3.0(100) 3 200 0.2( 9) 0.2(18) 0.4(35) 0.7( 74) 0.9(100) 1.3(100) 4 300 0 ( 6) 0 (13) 0 (25) 0 (52)0.2( 79) 0.2(100) 400 0 ( 4) 0 ( 9) 0 (17) 0 (31)0 ( 40) 0.2(52) 6 500 0 ( 2) 0 ( 4) 0 ( 7) 0 ( 9)0 ( 12) 0 ( 18) The di~solution in 32% nitric acid at room temperature i~ shown in Table 4 (with the values for copper again in brackets):
- 11- 20~8323 Inhibitory action of sodium sulfate on the dissolution of BSCC0 2212 and copper (...) in 32% nitric acid at room temperature Na2S04 Loss in weight (%) after (anhydrous) No.g ~ 15' 30' 1 h 2 h 4 h _ 1 100 0.51 (71) 1.7 (100) 4.4 (100) 9 (100) 20(100) 2<200+ 0.13 (38) 0 ( ~5) 0.12( 59) 3 ( 70) 9( 87) . .. . .. . _ _ . :, ., . :
+200 g of Na2S04 are no longer completely soluble in 32%
The~e experiments show that a combination of 20% nitric acid with 200 to 300 g of sodium sulfate are a sort of optlmum with which a still usable rate of dis~olution is accompanied by a good protective action. Of course, with continuous vi~ual inspection, 32% nitric acid with 100 g of sodium sulfate is also suitable. However, copper dissolves much more slowly in a solution saturated with sodium sulfa~e becauqe, with increasing dissolution of the copper, copper sulfate also crystallizes out im-mediately and readily deposits on the copper surface, inhibiting or rendering uneven the further dissolution.
Elevated temperature:
The effect of elevated temperature was examined in 10%
nitric acid:
Inhibitory action of NazS04 on the dissolution of BSCC0 2212 and copper in 10~ nitric acid at 70C (values for copper in brackets) Na2S04 Loss in weight (X) after (anhydrous) No. g~ 15' 30' 1 h 2 h 4 h 8 h 1 100 0.45(17) 0.77(32)1.1 (59)1.4(100)2.1(100) 2.9(100) 2 300 0 ( 3) 0.16( 7) 0.22(14)0.5( 27)0.7( 58) 0.7( 92) 3 500 0 ( 0) 0 ( 0)0 ( 0) - - -. . _ .. ._.
Here again favorable results are obtained with 100 to 300 g of sodium sulfate in a liter. They are e~sentiaLly equivalent to those which are obtained at room tempera-ture with 20% nitric acid.
In principle, other solutions which have the same effect as nitric acid are also conceivable:
a) Sulfuric acid + hydrogen peroxide b) Hydrochloric acid + hydrogen peroxide c) Hydrochloric acid + alkali chlorate - 13 Z0~L83Z3 The suitability of the combination of sulfuric acid with an oxidizing agent is demonstrated using 20~ sulfuric acid with 10% hydrogen peroxide at room tempexature. In this case, the addition of a sulfate is not necessary since the sulfate anions needed are provided by the sulfuric acid itself.
Differences in the dissolution of BSCC0 2212 and copper in 20% sulfuric acid with 10% H2O2 added at room temperature Tlme: 5~ 15~ 1 h 2 h 4 h Lo~s ~n weight of Cu/X 9.8 18 51 76 100 Los~ in weight of BSCCo/X 0.2 0.4 0.55 0.75 1.02 Example 1 (Comparative Example) A copper tube having a length of 10 cm, a wall thickness of 1 mm and an internal width of 8 mm, which contains a core composed of a qolidified BSCCO high-temperature superconductor melt of the formula Bi2Sr2CaCu20~, is placed in 20% nitric acid at room temperature and left there while stirring until the copper casing has been partlally etched away (2.8 h) and a part of the core is exposed.
The surface of the core exhibits deep holes and at the - 14 - 204~323 end faces, where the core was exposed to the action of the nitric acid without protection, it is dissolved away over a width of several mm.
Example 2 Example 1 was repeated, but 300 g of sodium sulfate were dissolved in one liter of 20% nitric acid. After 3 hours no breakthrough of the core was-as yet observable and a dense white film which covered the original surface had formed at the exposed end faces. After 12 hours, the copper had been dissolved down and the entire core was then covered with the white thin covering layer. Signs of an uneven removal or pitting were not observed.
Example 3 A similar rod to that in Example 1 was brought into contact with 200 ml of 20% sulfuric acid to which 30 ml of 10 % by weight hydrogen peroxide, divided into three equal portions, was gradually added, in which process copper was dissolved. The ~olution was stirred by means of a magnetic stirrer and the temperature was 25C. Ater 15 hours of contact time the copper casing had been dissolved. The superconductor core exhibited no acid attack on its surface, which was uniformly covered with alkaline earth metal sulfate.
Claims (10)
1. A process for producing molded bodies from pre-cursors of oxidic high-temperature superconductors of the BSCCO type, which comprises treating a copper mold of the desired shape which encloses a solidi-fied bismuth strontium calcium cuprate melt with a solution of a soluble compound containing sulfate anions, an aqueous mineral acid and an oxidizing agent until the copper mold is dissolved.
2. A process as claimed in claim 1, wherein the sul-fates of sodium, potassium, ammonium, magnesium or zinc are used as soluble compound containing sulfate anions.
3. A process as claimed in claim 1, wherein hydro-chloric or phosphoric acid is used as mineral acid.
4. A process as claimed in claim 1, wherein hydrogen peroxide or alkali chlorate is used as oxidizing agent.
5. A process as claimed in claim 1, wherein nitric acid is simultaneously used as aqueous mineral acid and as oxidizing agent.
6. A process as claimed in claim 1, wherein sulfuric acid is simultaneously used as aqueous mineral acid and as compound containing sulfate anions.
7. A process as claimed in claim 5, wherein the copper mold is dissolved with a solution of aqueous nitric acid and sodium sulfate.
8. A process as claimed in claim 6, wherein the copper mold is dissolved with a solution of aqueous sulfuric acid and hydrogen peroxide.
9. A process as claimed in claim 1, wherein the treat-ment is carried out at 15 to 80°C.
10. A process as claimed in claim 1, wherein a copper mold is treated which encloses the solidified bismuth strontium calcium cuprate melt and has one or more openings.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4026015.1 | 1990-08-17 | ||
| DE4026015A DE4026015A1 (en) | 1990-08-17 | 1990-08-17 | METHOD FOR PRODUCING MOLDED BODIES FROM PRE-STAGES OF HIGH-TEMPERATURE OXIDERS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2048323A1 true CA2048323A1 (en) | 1992-02-18 |
Family
ID=6412388
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002048323A Abandoned CA2048323A1 (en) | 1990-08-17 | 1991-08-01 | Process for producing molded bodies from precursors of oxidic high-temperature superconductors |
Country Status (11)
| Country | Link |
|---|---|
| US (1) | US5362712A (en) |
| EP (1) | EP0477493B1 (en) |
| JP (1) | JPH04231385A (en) |
| KR (1) | KR920004305A (en) |
| CN (1) | CN1039855C (en) |
| AT (1) | ATE153012T1 (en) |
| CA (1) | CA2048323A1 (en) |
| DE (2) | DE4026015A1 (en) |
| ES (1) | ES2102988T3 (en) |
| GR (1) | GR3023859T3 (en) |
| NO (1) | NO305114B1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4302267A1 (en) * | 1993-01-28 | 1994-08-04 | Abb Research Ltd | Electroplating nickel@ (alloy) substrate with silver |
| ES2335303T3 (en) | 2006-03-16 | 2010-03-24 | Nexans | HIGH TEMPERATURE MAGNETIC SUPERCONDUCTOR BEARING. |
| JP6607837B2 (en) * | 2016-10-06 | 2019-11-20 | 三菱重工業株式会社 | Thermal barrier coating film, turbine member and thermal barrier coating method |
Family Cites Families (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2414226A (en) * | 1944-01-27 | 1947-01-14 | Everett Samuel James | Method of making metal bonded abrasive tools |
| DE1253008B (en) * | 1964-08-22 | 1967-10-26 | Degussa | Process for etching copper foils for the production of printed circuits |
| US3429962A (en) * | 1965-12-01 | 1969-02-25 | Gen Electric | Method of forming a metallic oxide article |
| US3939241A (en) * | 1974-10-04 | 1976-02-17 | Crucible Inc. | Method for powder metallurgy compacting |
| US4025361A (en) * | 1975-09-04 | 1977-05-24 | Avco Corporation | Removal of ceramic investment shell mold from metal casting |
| DE2828762A1 (en) * | 1978-06-30 | 1980-01-10 | Philips Patentverwaltung | Etchant for thin copper layers in integrated circuits - consists of aq. soln. of ammonium persulphate contg. sulphuric acid and hydrogen peroxide |
| JPS59214602A (en) * | 1983-05-20 | 1984-12-04 | 日立造船株式会社 | Extrusion molding method of ceramics member |
| JPS6116807A (en) * | 1984-07-04 | 1986-01-24 | 三洋電機株式会社 | Manufacture of ceramic sheet |
| FR2621052A1 (en) * | 1987-09-25 | 1989-03-31 | Solvay | BATHS AND METHOD FOR CHEMICAL POLISHING OF COPPER SURFACES OR COPPER ALLOYS |
| DE3830092A1 (en) * | 1988-09-03 | 1990-03-15 | Hoechst Ag | METHOD FOR THE PRODUCTION OF A HIGH-TEMPERATURE SUPERCONDUCTOR AND MOLDED BODY THEREOF |
| US4976808A (en) * | 1989-04-22 | 1990-12-11 | Sumitomo Metal Mining Company Limited | Process for removing a polyimide resin by dissolution |
| US5215961A (en) * | 1990-06-25 | 1993-06-01 | The United States Of America As Represented By The Secretary Of The Navy | Machinable oxide ceramic |
-
1990
- 1990-08-17 DE DE4026015A patent/DE4026015A1/en not_active Withdrawn
-
1991
- 1991-07-16 EP EP91111809A patent/EP0477493B1/en not_active Expired - Lifetime
- 1991-07-16 DE DE59108701T patent/DE59108701D1/en not_active Expired - Fee Related
- 1991-07-16 AT AT91111809T patent/ATE153012T1/en not_active IP Right Cessation
- 1991-07-16 ES ES91111809T patent/ES2102988T3/en not_active Expired - Lifetime
- 1991-08-01 CA CA002048323A patent/CA2048323A1/en not_active Abandoned
- 1991-08-14 KR KR1019910013998A patent/KR920004305A/en not_active Application Discontinuation
- 1991-08-16 CN CN91105721A patent/CN1039855C/en not_active Expired - Fee Related
- 1991-08-16 JP JP3205931A patent/JPH04231385A/en active Pending
- 1991-08-16 NO NO913220A patent/NO305114B1/en unknown
-
1993
- 1993-06-23 US US08/081,855 patent/US5362712A/en not_active Expired - Fee Related
-
1997
- 1997-06-20 GR GR970401500T patent/GR3023859T3/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| ES2102988T3 (en) | 1997-08-16 |
| DE4026015A1 (en) | 1992-02-20 |
| CN1039855C (en) | 1998-09-16 |
| ATE153012T1 (en) | 1997-05-15 |
| KR920004305A (en) | 1992-03-27 |
| US5362712A (en) | 1994-11-08 |
| EP0477493A3 (en) | 1993-02-17 |
| NO913220D0 (en) | 1991-08-16 |
| DE59108701D1 (en) | 1997-06-19 |
| NO913220L (en) | 1992-02-18 |
| NO305114B1 (en) | 1999-04-06 |
| CN1059226A (en) | 1992-03-04 |
| EP0477493A2 (en) | 1992-04-01 |
| EP0477493B1 (en) | 1997-05-14 |
| GR3023859T3 (en) | 1997-09-30 |
| JPH04231385A (en) | 1992-08-20 |
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